|
This is why I use 38V as the default setting on the Landis Charger controller: >From the Battery University website ( http://batteryuniversity.com/partone-13.htm ): State-of-charge reading based on terminal voltage The state-of-charge of a lead-acid battery can, to a certain extent, be estimated by measuring the open terminal voltage. Prior to measuring, the battery must have rested for 4-8 hours after charge or discharge and resided at a steady room temperature. A cold battery would show slightly higher voltages and a hot battery would be lower. Plate additions of calcium and antimony will also vary the open terminal voltage with calcium being a little higher than antimony. Furthermore, AGM has a higher voltage plateau than the flooded lead acid and the readings on Figure 3 may not apply for AGM systems. Due to surface charge, a brief charge will raise the terminal voltage and provide inflated state-of-charge reading. For example, a 30 minute charge could wrongly indicate 100% SoC if no rest is applied. With sufficient rest and stable temperature, voltage measurements provide an amazingly accurate SoC estimation for lead acid batteries. It is important that the battery is free of polarization. If connected in a system, such as in a car, there are steady auxiliary loads, not to mention frequent starting and driving.
Note: The BCI readings apply to flooded batteries with antimony doping. Calcium will raise the voltage by 5 - 8%. Calcium is commonly used for maintenance-free lead acid batteries. After charge or discharge, allow the battery to rest for a minimum of eight hours before assessing the state-of-charge by measuring the terminal voltage. Harry Landis > Date: Thu, 23 Apr 2009 09:42:02 -0400 > From: msbriggs alberti unh edu > To: jjcrmc verizon net > CC: elec-trak cosmos phy tufts edu > Subject: Re: (ET) Fully charged pack voltage > > > On Thu, 23 Apr 2009, John J Casey wrote: > > > In my experience, the onboard ge charger takes my newish T-105's up to > > 44-45v over an 18 hour cycle, the last 3-5 hrs between 44.4 and 45v for cell > > equalization. End the charge cycle and in a short time the voltage settles > > back to 39v.Jack > > So, the fully charged pack then has a voltage of 39 V (since that is what > it settles to after charging). > One thing that is troubling me - what does it take a while for the > battery's voltage to gradually drop from the elevated charging voltage > down to its resting voltage. I know that while charging the voltage > applied will be higher than the battery's voltage due to the voltage drop > across the internal resistance of the battery (batteries) - but once the > charger turns off, I would think that the battery pack voltage would drop > rather immediately down to its resting voltage (the potential difference > that the chemical reactions taking place at the electrodes produce). > BTW, this has some interesting information about how the internal > resistance of the electrolyte changes with state of charge, which gives > lead acid batteries their unique voltage vs. state of charge curves: > http://www.arttec.net/Solar_Mower/4_Electrical/Battery%20Charging.pdf > The main thing I'm trying to figure out right now is what to set > my Landis charge controller to to make sure that the pack gets fully > charged (and doesn't take 3 days to get there). It would seem that the > default 38V setting is too low, since the pack should be higher than > that when fully charged. > > Thanks, > Mike > > > On Apr 23, 2009, at 8:13 AM, Michael S Briggs wrote: > > > > > > I just got a nice new pack of Trojan T-605s (slightly lower > > capacity than T-105s, with a proportionately lower price). I'm > > trying to figure out what the voltage of a fully charged new > > pack *should* be, and I have seen very different things as > > skimming through the archives. > > My understanding is that the chemical reactions taking place in > > a lead-acid cell produce a potential difference of 2.13 Volts, > > so a fully charged lead-acid battery measured with a very high > > impedance voltmeter should measure that 2.13 Volts per cell, or > > 6.39V for a 6V battery, and 38.34 V for a 36V pack. > > But, I have seen statements in the archives saying that a fully > > charged pack should have a voltage of 42V or so (various posts > > saying anywhere from about 40V up to 44V). > > > > Thanks, > > Mike > > > > -- > > > > -------------------------------------------------------------- > > Michael S. Briggs, PhD > > UNH Physics Department > > (603) 862-2828 > > --------------------------------------------------------------- > > > > > > _______________________________________________ > > Elec-trak mailing list > > Elec-trak cosmos phy tufts edu > > https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak > > > > > > > > |